1. Field of the Invention
The invention is based on a preinjection valve for controlling the fuel inflow of a fuel injection valve.
2. Description of the Prior Art
A preinjection valve of the type with which this invention is concerned is described in German Published, Nonexamined Patent Application DE 40 21 453 A1. In such a preinjection valve, an inlet conduit communicates with a high-pressure fuel pump, which pumps fuel at high pressure into the inlet conduit. A preinjection valve member is disposed sealingly in a bore that communicates with the inlet conduit, so that one side is acted upon by the fuel pressure of the inlet conduit. When the pressure in the inlet conduit reaches a certain level, the preinjection valve member moves counter to a closing force as far as a stop and thereby pumps a fixedly predetermined preinjection quantity into an outlet conduit that communicates with the fuel injection valve. The preinjection valve furthermore has a deflection valve member, which is sealingly guided in a second bore and one face end of which also communicates with the inlet conduit. After the preinjection quantity has been pumped by the preinjection valve member, the fuel pressure in the inlet conduit rises still more. When a threshold pressure for the main injection is reached, the deflection valve member moves counter to a closing force and thereby enables the communication from the inlet conduit to the outlet conduit, which communicates with the injection valve. The fuel flows to the fuel injection valve via the outlet conduit until such time as the deflection valve member closes again as a result of a drop in the fuel pressure in the inlet conduit, and the injection is terminated.
The known preinjection valve has the disadvantage that two guide bores must be made, one each for the preinjection valve member and the deflection valve member. This makes a compact design of the preinjection valve more difficult and necessitates at least one branch of the inlet conduit coming from the high-pressure pump, and this branch has to be rounded, which is complicated.
The preinjection valve of the invention for controlling the fuel inflow of a fuel injection valve has the advantage over the prior art that a compact design of the preinjection valve is possible, thus enabling the preinjection valve to be built into either the inlet conduit of the fuel injection valve or inside the fuel injection valve. Because of the disposition of the preinjection valve member in the same inlet conduit as the deflection valve member, there is no need to form a complicated branch in the inlet conduit.
In an advantageous feature of the subject of the invention, the preinjection valve member is embodied as a ball, which is guided sealingly in the inlet conduit and is braced, via a closing spring, on the pistonlike deflection valve member. The deflection valve member extends as far as the inside of a spring chamber, where it merges with a spring plate. Between the spring plate and the opposed wall of the spring chamber, a closing spring is disposed with prestressing. A compensation disk is disposed between the face end of the spring chamber, toward the preinjection valve member, and the spring plate. By varying the thickness of this compensation disk, the preinjection quantity of the preinjection valve member can advantageously be changed easily. By means of a suitable design of the closing springs, the opening pressure of the preinjection and main injection can be set, and thus for a given course over time of the pressure rise in the inlet conduit in the injection, the time interval between the preinjection and the main injection can also be set.